FIG. 6 is a block diagram illustrating a controlling apparatus for a three-phase synchronous motor that includes an incorrect wiring detecting function. In FIG. 6, a torque command generation unit 1 calculates a torque command value TCMD from a deviation between a velocity command value Vc and a feedback velocity signal VcF. A current command generation unit 2 calculates, according to the torque command value TCMD, a q-axis current command value IqC and a d-axis current command value IdC, which are input to an armature current supplying apparatus 3.
The armature current supplying apparatus 3 includes a power converter 3e, such as an inverter, from which three-phase output voltage is supplied to a synchronous motor M. The synchronous motor M has an encoder 6 attached thereto, and a rotor position signal θm is input to a feedback velocity signal generation unit 7 so as to generate the feedback velocity signal VcF.
A current detector 4 is provided on the input side of the synchronous motor M, and current signals Iu and Iv of a U phase and V phase detected by the current detector 4 are input to an orthogonal two-axis transformation unit 5. Using a SIN signal and COS signal generated by a signal generator (OSC) 9 according to the rotor position signal θm, the orthogonal two-axis transformation unit 5 converts the current signals Iu and Iv into a d-axis current feedback signal IdF and a q-axis current feedback signal IqF.
In the armature current supplying apparatus 3, current controllers 3a and 3b calculate a q-axis voltage command value VqC and a d-axis voltage command value VdC for eliminating a deviation between the current command value IqC and the feedback signal IqF and a deviation between the current command value IdC and the feedback signal IdF. The voltage command values VqC and VdC are input to a coordinate converter 3c. 
Using the SIN signal and the COS signal, the coordinate converter 3c converts the voltage command values VqC and VdC into a three-phase voltage command value VUC, VVC, VWC, and supplies the three-phase voltage value to a PWM controller 3d. 
The PWM controller 3d PWM-controls the power converter 3e using a drive signal generated from the voltage command value VUC, VVC, VWC and drives the synchronous motor M by converting a DC voltage into a three-phase AC voltage.
In FIG. 6, an incorrect wiring detection unit 8 is provided that detects incorrect two-phase wiring or incorrect three-phase wiring of the phase sequence of the synchronous motor M with respect to an output phase of the power converter 3e. In the presence of incorrect two-phase wiring or incorrect three-phase wiring, the q-axis current command value IqC is in a saturated state, the q-axis current feedback signal IqF becomes a predetermined value or higher, and the polarities of the q-axis current feedback signal IqF and feedback velocity signal VcF are reversed. By paying attention to these, the incorrect wiring detection unit 8 detects incorrect wiring and outputs an alarm signal AS.
As depicted in FIG. 7, the incorrect wiring detection unit 8 consists of a saturated state determination unit 8a, a q-axis current feedback signal determination unit 8b, an integration unit 8c, and a determination unit 8d. 
With reference to FIGS. 7 and 8, the following will describe an operation of detecting two-phase incorrect wiring of a phase sequence performed by the incorrect wiring detection unit 8 (e.g., a situation in which an input phase of the synchronous motor M is connected in a phase sequence of U-W-V to an output phase U-V-W of the power converter 3e).
The saturated state determination unit 8a determines that the q-axis current command value IqC has been put in a saturated state as depicted in FIG. 8B, and outputs the determination result to the integration unit 8c. The q-axis current feedback signal determination unit 8b determines that the q-axis current feedback signal IqF is a predetermined value or higher, and outputs the determination result to the integration unit 8c. At a moment at which the q-axis current feedback signal IqF is determined to have a positive polarity, the integration unit 8c starts to integrate, as depicted in FIGS. 8A, 8C, a period of time of a negative polarity of the feedback velocity signal VcF that oscillates without following the velocity command Vc, and outputs the integrated period as an integrated value IV. As depicted in FIGS. 8C, 8D, at a moment at which the integrated value IV reaches a cumulative time RT, the determination unit 8d outputs an alarm signal AS for reporting incorrect wiring.
However, in a case where a plurality of induction motors connected in parallel to each other and mechanically coupled to each other are driven by one power converter, even if a phase sequence of one motor includes incorrect wiring, the motor in the wrong-wiring state will be driven due to the influence of output torque of the motors with correct wiring. As a result, a load velocity becomes adjustable in conformity with a command value. Accordingly, a prior art relying on velocity and/or velocity command values is inapplicable to a plurality of induction motors.
Existing methods do not include a method of detecting incorrect wiring to be used when a plurality of motors are driven by a power converter, and are incapable of solving a problem that occurs when a plurality of motors include one with incorrect wiring, as described above.